This type of proportional directional control valve is the subject matter of Published Unexamined German Patent Application DE 10 2011 003 556 A1, for example. A control valve, designed as a central valve, for controlling the inflow and outflow of hydraulic medium to and from a camshaft adjustment device is provided. A control piston is axial displaceably situated in the plastic valve housing, a locking ring being provided for the form-locked fixing of the valve housing in a camshaft or in a rotor of the camshaft adjustment device. The locking ring has a radially extending circumferential section that is designed for engaging with an annular groove formed in the camshaft or the rotor.
Another central valve of this type is provided in DE 10 2012 220 830 A1. A control piston is axially displaceably guided within a sleeve that is extrusion-coated with plastic. The guide sleeve in turn is situated in a housing that is designed as a central screw, and is secured in position with the aid of a locking ring inserted into a groove. The movability of the control piston is limited on the one hand by a sleeve base, and on the other hand by a stop element. The stop element is designed as a component that is separate from the guide sleeve and joined to the sleeve in an integrally bonded or form-locked manner, for example with the aid of a snap connection.
A central valve that includes a two-part central screw is provided in DE 10 2013 203 951 A1. The central screw is made up of a screw shank and a screw sleeve that is designed as a deep-drawn part. A control piston situated in a guide sleeve extrusion-coated with plastic is contactable with a stop element, the stop element being a locking ring which is inserted into a groove in the screw sleeve and at the same time fixes the guide sleeve within the screw sleeve.
Another housing of a central valve, which arises from a deep-drawing process, is provided in DE 10 2012 202 520 A1. A central valve for a camshaft adjuster, including a control piston that is axially movably guided within a valve housing, is provided. The housing is manufactured by a deep-drawing process, and is designed as a screw that includes a screw head, a screw shank, and a thread. The screw head of the housing includes a collar with a flange surface that may be supported on the camshaft adjuster. The screw head also includes a contact surface for an assembly tool.